A conventional grinder has a rotary shaft on which a grinding tool such as a grinding disc or a buffing disc is mounted for grinding a work piece.
In operation, it is necessary to frequently replace the grinding tool. Conventionally, when replacing the grinding tool, a hand tool is used to fix the rotary shaft and prevent the rotary shaft from rotating. Under such circumstance, the grinding tool can be replaced.
However, it is inconvenient to fix the rotary shaft with a specific hand tool. In addition, a user must carry and store the hand tool. In order to solve this problem, the inventor had designed grinders with different kinds of mechanisms for chucking the rotary shaft so that the grinding tool can be easily replaced without using any hand tool. The invention is designed under the same purpose.